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 Testing Valves
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 Return to top of page · Post #: 1 · Written at 5:32:43 PM on 9 October 2017.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 382

I have been testing some valves with my Valve tester. 10 x 6J6 valves were good. 6J6 is a Twin Triode.

1 x 6J6 has no shorts, heater on. Had an initial Plate current, but slowly reduced to zero ... both Triodes had zero Plate current.

Nothing to loose ... so I gently increased the Grid voltage. ie less negative .... beyond the recommended test voltage. Got a small Plate current, but also a purple glow and a noise from the valve .... then Tester cutout triggered. Both Triodes generate a similar result.

I am assuming that this glow and noise indicate a “gassy” tube?? Hence stuffed??


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
 Return to top of page · Post #: 2 · Written at 6:11:26 PM on 9 October 2017.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 335

Definitely looks like a loss of vacuum.
Fairly common with high stress TV valves back in the good old BW days.
JJ


 
 Return to top of page · Post #: 3 · Written at 6:37:47 PM on 9 October 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5341

Yes, the blue glow is usually an indication of gone gassy.


 
 Return to top of page · Post #: 4 · Written at 9:45:22 PM on 9 October 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3860

Nomenclature issue: If you increase the grid voltage you make it more Negative: Making it more negative gradually cuts it off.

If you decrease the grid 1 voltage to the point of it going positive it then becomes a diode, which may present as a short.

If you increase the voltage between heater & cathode, depending on the valve, that may causes a heater cathode "flash over".

A Blue glow (normally dark {Electric} blue) inside the plates OK: Pastel blue, outside the plates: Gassy.

Holding the "Test" button down too long can damage some valves in some testers.


 
 Return to top of page · Post #: 5 · Written at 8:36:50 AM on 10 October 2017.
BringBackTheValve's Gravatar
 Location: Linton, VIC
 Member since 30 December 2016
 Member #: 2028
 Postcount: 229

Regarding blue glow;

Plasma!

This is a good sign. It means the valve has a very high vacuum.


 
 Return to top of page · Post #: 6 · Written at 10:31:52 AM on 10 October 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3860

Now this is a bit like "Oils ain't oils". Some valves actually have a label saying where the "Plasma" flow is. Note my comment "Electric Blue" is a much darker, toward Navy blue. The gassy blue is more toward a sky or baby blue and the both occur in a different position.


 
 Return to top of page · Post #: 7 · Written at 2:06:10 PM on 10 October 2017.
BringBackTheValve's Gravatar
 Location: Linton, VIC
 Member since 30 December 2016
 Member #: 2028
 Postcount: 229

Yep, I'll buy that Marcc.

The blue that comes with very good vacuum is deep violet, and within the plate area.


 
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